1. Field of the Invention
The present invention relates to a sintered polycrystalline diamond composite for use in rock drilling, machining of wear resistant metals, and other operations which require the high abrasion resistance or wear resistance of a diamond surface. Specifically, this invention relates to such bodies which comprise a polycrystalline diamond layer attached to a cemented metal carbide substrate via processing at ultrahigh pressures and temperatures.
2. Prior Art
It is well known to sinter a mass of polycrystalline particles such as diamond or cubic boron nitride in the presence of a suitable solvent catalyst by means of a high pressure, high temperature apparatus to form a compact with good particle-to-particle bonding. While such compacts have good abrasion characteristics, they lack the required transverse rupture strength and are, therefore, not suitable for certain cutting operations due to the difficulty in attaching them to a tool holder which would provide the required mechanical strength. U.S. Pat. No. 3,745,623 U.S. Pat. No. Re. 32,380 solves this problem by sintering a mass of polycrystalline particles in conjunction with a tungsten carbide substrate to produce a composite compact in which the particles are directly bonded to each other and to a cemented carbide substrate. Such composite compacts are widely used in machining and drilling since the carbide substrate provides good mechanical support and can be clamped or brazed to a suitable tool holder or drilling bit.
Although compacts produced by these prior art techniques have excellent abrasion resistance and good mechanical strength, they are limited to applications where temperatures do not exceed 700.degree. C. to 800.degree. C. for excessive periods of time. This is a result of degradation by chemical reactivity and thermal expansion of the entrapped catalytic metals, such as cobalt or other group 8 metals which are used to synthesize diamond crystals and to sinter these crystals into a polycrystalline mass.
One solution to this problem is to form diamond or diamond-like carbon films on substrate metals, which have high transverse rupture strength, by various chemical vapor deposition methods. This produces a carbon surface that does not contain catalytic or other reactive metals in its interstices. At present, many scientists throughout the world are performing research and development to produce cutters of this type. However, the problem still to be solved is obtaining a strong bond between the diamond or diamond-like carbon and the substrates. State of the art substrates coated in this manner show widely varied bond strengths which are, at best, not suitable for harsh industrial applications, such as rock drilling.